In Annie the song is an advert for toothpaste, nothing to do with having a nice personality really, I think that's just an interpretation that it's nice for Annie to make as she will never have the nice clothes but she can smile.
Are men exhorted to smile and be nice? I've never heard anyone yell 'give us a smile luv to a man/boy on the street. Or language policed when they aren't thought to be kind and inclusive enough.
I'm all for smiling when you actually want to, and do think that smiles can be infectious and bring good mental health but I have been yelled at for not looking happy enough, and also got in trouble for looking friendly rather than putting my best 'not interested' face on so I get people's concerns. Even if the OP might well have been a GF.